Abstract A kinetic study of photopolymerization on dental nanocomposites was carried out, based on measurements of spectroscopy RTIR in mode ATR .
During this study, the grafting of a trialcoxysilane, 3-méthacryloyloxypropyl-triméthoxysilane (3-MPS), at the surface of the nanoparticules was implemented according to two processes sol-gel: the conventional and the photoinitiated. The use of organosilanes carrying functions methacrylate is a process making it possible to create covalent bonds between a mineral filler, comprising on its surface of the functions hydroxyl, and the organic matrix. The functionalized fillers were characterized by FTIR and TGA.
A comparative study of spectra FTIR of the 3-MPS alone, of the filler before and after functionnalization was carried out.
Whatever the process of grafting used, the spectra IR of the fillers grafted by the 3-MPS show the disappearance of the band to 2840 cm-1(CH 3 - symmetrical elongation) characteristic of the functions Si-O-Me, proving that the reaction of hydrolysis took place, and the appearance of two new absorption bands to 1637 and 1714 cm-1 which characterize, respectively, C=C band of the methacrylate and C=O band of the carbonyl present in the 3-MPS.
The presence of organic matter on the surface of the filler was confirmed by thermogravimetric analysis. We noticed, for the two processes of grafting, a loss of mass which is added to that observed on the non functionalized fillers. This loss of mass corresponds to the degradation of the 3-MPS grafted on the surface of the fillers. The absence of loss of mass towards 152°C (temperature boiling of the 3-MPS) confirms the absence of not grafted 3-MPS molecules.
Although the results obtained by FTIR and TGA make it possible to confirm the establishment of covalent bonds between the 3-MPS and the fillers, measurements of hardness of the composites containing these functionalized fillers may suggest that the grafting by photochemical way is not carried out in a homogeneous way on the fillers.
The study of the photopolymerization of these composites made it possible to show that the modification of the surface of the fillers has little influence on the kinetics of the photopolymerization. On the other hand, it modifies significantly the mechanical properties of the composite. The incorporation of nanocharges slows down the kinetics of photopolymerization of the resin Bis-GMA/TEGDMA because of phenomenon of diffusion of the light.
Key words: Dental composite, mineral filler , kinetics , photopolymerization, organic matrix
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